The present invention relates to Planar Inverted F-Antenna (PIFA), and more particularly, PIFA antenna with non-conventional shapes and an integrated feed line on a ground plane:
In wireless radio frequency (xe2x80x9cRFxe2x80x9d) data communications there is currently a shift in the requirement from the existing single band operation to dual industrial scientific medical (xe2x80x9cISMxe2x80x9d) band operation covering, for example, frequency ranges of 2.4-2.5 to 5.15-5.35 GHz. Generally, dual ISM band operation can be accomplished using either external or internal antennas. External antennas are large and susceptible to mechanical damage. Conversely, internal antennas are unseen by the user, smaller, and less susceptible to mechanical damage. However, internal antenna are constrained in effectiveness because of the size and volume restrictions associated with wireless devices
In most of the devices, only specified regions with defined volume can accommodate the placement of internal antennas. These regions are usually not of perfect rectangular/square shape or of large size. At times, the available space for internal antennas nearly assumes a circular cylindrical shape of very small area and volume. For optimal performance of the internal antenna, it is desirable that the shape of the radiating structure of the antenna use as much of the allowed area as possible. Dual band ISM internal antenna, however, are generally rectangular in shape, which will be explained in connection with FIG. 9, below. Thus, it would be desirous to develop a non-conventionally shaped PIFA antenna to use more of the available space for internal antenna.
There seems to be no work reported on circular shaped either single or dual band PIFAs in open literature Wen-Hsiu Hsu and Kin-Lu Wong, xe2x80x9cA Wideband Circular Patch Antennaxe2x80x9d, MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Vol. 25, No. 5, Jun. 5, 2000 pp. 328 (hereinafter referred to as Hsu et al) reports a dual band microstrip antenna with a circular radiating element using an air-substrate. The dual frequency operation of the microstrip antenna of Hsu et al is realized through two separate linear slots. The two slots are placed symmetrically with respect to the central axis of the radiating element. The axis of the microstrip feed line is also parallel to the axes of the slots.
A dual frequency circular microstrip antenna with a pair of arc-shaped slots has been studied in Kin-Lu Wong and Gui-Bin Hsieh, xe2x80x9cDual-Frequency Circular Microstrip Antenna with a Pair of Arc-Shaped Slotsxe2x80x9d, MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Vol. 19, No. 6, Dec. 20 1998, pp. 410-412 (hereinafter referred to as Wong et al). The two arc-shaped slots are located on either side of one of the central axes. In the work of Wong et al, the two arc-shaped slots are also symmetrically placed with respect to the referred central axis of the antenna.
In both of the above research papers, the size of the radiating element corresponds to half wavelength at the center frequency of the lower resonant band.
Circular patch antennas also provide some insight into the present invention. The case studies of circular patches with a single arc or U-shaped slot are described in the work of K. M. Luk, Y. W. Lee, K. F Tong, and K. F. Lee, xe2x80x9cExperimental studies of circular patches with slotsxe2x80x9d, IEEE Proc.xe2x80x94Microw. Antennas Propagation, Vol. 144, No. 6, December 1997, pp. 421-424 (hereinafter referred to as Luk et al). With a single arc shaped slot, the choice of center or offset feed determines the dual or single frequency operation. The choice of a U-shaped slot, as in the paper of Luk et al, results only in a single band operation with a wider impedance bandwidth.
Recently there has been a drastic increase in the demand for use of internal antennas in wireless applications. In a variety of options for internal antennas, PIFAs seems to have a greater potential. Apart from extensive utility of PIFA in commercial cellular communications, PIFA continues to find its usefulness in many other systems applications such as WLAN, the Internet, or the like The printed circuit board of the communication device serves as the ground plane of the internal antenna. The PIFA is characterized by many distinguishing properties such as relative lightweight, ease of adaptation and integration into the device chassis, moderate range of bandwidth, versatile for optimization, and multiple potential approaches for size reduction. Its sensitivity to both the vertical and horizontal polarization is of immense practical importance in wireless devices because of multi path propagation conditions. All these features render the PIFA to be as good a choice as any internal antenna for wireless device applications. When it comes to diversity schemes, PIFAs have a unique advantage because it can be fashioned into varieties of either Polarization or pattern Diversity schemes.
A conventional single band PIFA assembly is illustrated in FIGS. 9A and 9B. The PIFA 110 shown in FIG. 9A and FIG. 9B consists of a radiating element 101, a ground plane 102, a connector feed pin 104a, and a conductive post or pin 107. A power feed hole 103 is located in radiation element corresponding to connector feed pin 104a. Connector feed pin 104a serves as a feed path for RF power to the radiating element 101. Connector feed pin 104a is inserted through the feed hole 103 from the bottom surface of the ground plane 102. The connector feed pin 104a is electrically insulated from the ground plane 102 where the pin passes through the hole in the ground plane 102. The connector feed pin 104a is electrically connected to the radiating element 101 at point 105a with, for example; solder. The body of the feed connector 104b is electrically connected to the ground plane at point 105b with, for example, solder The connector feed pin 104a is electrically insulated from the body of the feed connector 104b. A through hole 106 is located in radiation element 101 corresponding to conductive post or pin 107. Conductive post 107 is inserted through the hole 106. The conductive post 107 serves as a short circuit between the radiating element 101 and ground plane 102. The conductive post 107 is electrically connected to the radiating element 101 at point 108a with, for example, solder. The conductive post 107 is also electrically connected to the ground plane 102 at point, 108b with, for example, solder. The resonant frequency of the PIFA 110 is determined by the length (L) and width (W) of the radiating element 101 and is slightly affected by the locations of the feed pin 104a and the shorting pin 107. The impedance match of the PIFA 110 is achieved by adjusting the diameter of the connector feed pin 104a, by adjusting the diameter of the conductive shorting post 107, and by adjusting the separation distance between the connector feed pin 104a and the conductive shorting post 107. The fundamental limitation of the configuration of the PIFA 110 described in FIG. 9A and FIG. 9B is the requirement of relatively large dimensions of length (L) and width (W) of the radiating element 101 to achieve desired resonant frequency band. This configuration is limited to only single operating frequency band applications. If PIFA was a dual band PIFA, a slot (not shown) would reside in radiating element 101 to quasi partition the radiating element 101.
As represented by FIGS. 9A and 9B, the majority of PIFA designs focus on PIFA designs having a rectangular or square shape. Thus, it would be desirous to develop a compact dual ISM band internal PIFA having a non-conventional shapes.
This invention presents new schemes of designing circular shaped PIFAs with a small ground plane. Deviating distinctly from the routine and conventional feed structure usually employed in PIFA design, this invention also demonstrates that the RF feed line system can be integrated to the PIFAs.
To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, planar inverted F antennas are disclosed. The planar inverted F antennas include non-rectangular radiating elements residing on a dielectric carriage, which in turn resides on a ground plane A slot in the radiating element quasi partitions the radiating element. A feed pin, conducting post, and matching stub are used to feed power to the radiating element and tune the PIFA to the appropriate frequency.